Electrode for energy storage device

ABSTRACT

Particles of active electrode material are made by blending or mixing a mixture of activated carbon, optional conductive carbon, and binder. In selected implementations, the activated carbon particles have between about 70 and 98 percent microporous activated carbon particles and between about 2 and 30 percent mesoporous activated carbon particles by weight. Optionally, a small amount of conductive particles, such as conductive carbon particles may be used. In one implementation, the binder is inert. The electrode material may be attached to a current collector to obtain an electrode for use in various energy storage devices, including a double layer capacitor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.60/852,459, filed by Linda Zhong and Xiaomei Xi on 17 Oct. 2006, whichis hereby incorporated by reference as though fully set forth herein.

BACKGROUND

The present invention generally relates to electrodes and thefabrication of electrodes. More specifically, the present inventionrelates to electrodes used in energy storage devices, such aselectrochemical double layer capacitors and hybrid capacitor and batterydevices.

Electrodes are widely used in many devices that store electrical energy,including primary (non-rechargeable) battery cells, secondary(rechargeable) battery cells, fuel cells, and capacitors. Importantcharacteristics of electrical energy storage devices include energydensity, power density, maximum charging and discharging rate, internalleakage current, equivalent series resistance (ESR), and/or durability,i.e., the ability to withstand multiple charge-discharge cycles. For anumber of reasons, double layer capacitors, also known assupercapacitors and ultracapacitors, are gaining popularity in manyenergy storage applications. The reasons include availability of doublelayer capacitors with high power densities (in both charge and dischargemodes), and the long life of double layer capacitors compared toconventional rechargeable cells.

Double layer capacitors typically use as their energy storage elementelectrodes immersed in an electrolyte (an electrolytic solution). Assuch, a porous separator immersed in and impregnated with theelectrolyte may ensure that the electrodes do not come in contact witheach other, preventing electronic current flow directly between theelectrodes. At the same time, the porous separator allows ionic currentsto flow through the electrolyte between the electrodes in bothdirections. As discussed below, double layers of charges are formed atthe interfaces between the solid electrodes and the electrolyte.

When electric potential is applied between a pair of electrodes of adouble layer capacitor, ions that exist within the electrolyte areattracted to the surfaces of the oppositely-charged electrodes, andmigrate towards the electrodes. A layer of oppositely-charged ions isthus created and maintained near each electrode surface. Electricalenergy is stored in the charge separation layers between these ioniclayers and the charge layers of the corresponding electrode surfaces. Infact, the charge separation layers behave essentially as electrostaticcapacitors. Electrostatic energy can also be stored in the double layercapacitors through orientation and alignment of molecules of theelectrolytic solution under influence of the electric field induced bythe potential. This mode of energy storage, however, is secondary.

In comparison to conventional capacitors, double layer capacitors havehigh capacitance in relation to their volume and weight. There are twomain reasons for these volumetric and weight efficiencies. First, thecharge separation layers are very narrow. Their widths are typically onthe order of nanometers. Second, the electrodes can be made from aporous material, having very large effective surface area per unitvolume. Because capacitance is directly proportional to the electrodearea and inversely proportional to the widths of the charge separationlayers, the combined effect of the large effective surface area andnarrow charge separation layers is capacitance that is very high incomparison to that of conventional capacitors of similar size andweight. High capacitance of double layer capacitors allows thecapacitors to receive, store, and release large amount of electricalenergy.

Electrical energy stored in a capacitor is determined using a well-knownformula:

$\begin{matrix}{E = {\frac{C*V^{2}}{2}.}} & (1)\end{matrix}$

In this formula, E represents the stored energy, C stands for thecapacitance, and V is the voltage of the charged capacitor. Thus, themaximum energy (E_(m)) that can be stored in a capacitor is given by thefollowing expression:

$\begin{matrix}{{E_{m} = \frac{C*V_{r}^{2}}{\;}},} & (2)\end{matrix}$

where V_(r) stands for the rated voltage of the capacitor. It followsthat a capacitor's energy storage capability depends on both (1) itscapacitance, and (2) its rated voltage. Increasing these two parametersmay therefore be important to capacitor performance.

SUMMARY

Over a number of charge-discharge cycles, ions within an electrolyte ofan energy storage device may migrate within an electrode of the energystorage device. Over time, ions may get “stuck” within pores (e.g.,micropores) of an electrode and become unavailable for furthercharge—discharge cycles. This reduction in available ions within alocalized region of the electrode results in a condition of “localelectrolyte starving” in that region of the electrode. As regions of anelectrode lose the availability of ions in those regions, the energystorage device undergoes a reduction in performance. It would bedesirable to improve reliability and durability of energy storagedevices, as measured by the number of charge-discharge cycles that anenergy storage device can withstand without a significant deteriorationin its operating characteristics. Additionally, it would be desirable toprovide energy storage devices using these electrodes.

The use of both microporous and mesoporous activated carbons together isprovided. The mesoporous activated carbons provide excess capacity forelectrolytes (and the ions within the electrolytes). Microporousactivated carbons, however, have smaller capacities for electrolytes andions. Thus, when ions may not be available due to the microporousactivated carbons, the mesoporous activated carbons may provideadditional electrolyte in a localized region to provide additional ionsfor charge—discharge cycles.

In a double layer capacitor, for example, local electrolyte starvationcan lead to capacitance fade, where the capacitance of the double layercapacitor decreases over multiple charge-discharge cycles. It would bedesirable to improve reliability and durability of energy storagedevices double layer capacitors, as measured by the number ofcharge-discharge cycles that a double layer capacitor can withstandwithout a significant deterioration in its operating characteristics(e.g., capacitance). Since an end of life of a double layer capacitorcan be defined for a particular application by reaching an unacceptablecapacitance level for that application, slowing a fade in capacitancecan directly increase the life of a double layer capacitor.

Various implementations hereof are directed to methods, electrodes,electrode assemblies, and electrical devices that may be directed to ormay satisfy one or more of the above needs. An exemplar implementationherein disclosed is a method of making particles of active electrodematerial. In accordance with such a method, particles of activatedcarbon, optional conductive carbon, and binder may be mixed. In aspectshereof, the activated carbon may comprise between about 70 and 98percent microporous activated carbon particles and between about 2 and30 percent mesoporous activated carbon particles by weight. In aspectshereof, the optional conductive particles may include conductive carbonmaterials such as carbon black, graphite, carbon fiber, carbonnanotubes, and the like.

In accordance with some alternative aspects hereof, the binder is anelectrochemically inert binder, such as PTFE. The proportion of theinert binder may be between about 3 and about 20 percent by weight, andin some other instances between about 9 and about 11 percent by weight,or may be, for example, about 10 percent by weight. In accordance withsome aspects hereof, the proportion of the optional conductive particlesin the resultant mixture may be between about 0 and about 15 percent byweight, and in some instances does not exceed about 0.5 percent byweight. In accordance with further alternative aspects hereof, mixing ofthe activated carbon, optional conductive carbon, and binder may beperformed by dry-blending these ingredients. In accordance with somefurther alternative aspects hereof, the mixing may be carried out bysubjecting the activated carbon, optional conductive carbon, and binderto a non-lubricated high-shear force technique. In accordance with stillfurther alternative aspects hereof, films of active electrode materialmay be made from the particles of active electrode material made as isdescribed herein. The films may be attached to current collectors andused in various electrical devices, for example, in double layercapacitors. Other binders that may be used include, but are not limitedto, polyvinylidene difluoride (PVDF), polyethylene (PE), high molecularweight polyethylene (HMWPE), ultra high molecular weight polyethylene(UHMWPE), polypropylene (PP), carboxymethyl cellulose (CMC),polyvinylphenol, polyvinylpyrrolidine, polyvinyl acetate, polyvinylalcohol, and polyacetylene.

In one implementation, a method of making particles of active electrodematerial may include providing activated carbon with between about 70and 98 percent microporous activated carbon particles and between about2 and 30 percent mesoporous activated carbon particles by weight;providing binder; mixing the activated carbon and the binder to obtain amixture. The method may in some options further include providingconductive particles, such as conductive carbon particles. In oneimplementation, the binder may be or may include PTFE. In oneimplementation, the operation of mixing may include dry blending theactivated carbon, conductive carbon, and the binder. In oneimplementation, the operation of mixing may be performed withoutprocessing additives. In another implementation, the operation of mixingmay be performed with one or more processing additives.

In one implementation, an electrode may include a current collector; anda film of active electrode material attached to the current collector,wherein the active electrode material may include particles of activatedcarbon with between about 70 and 98 percent microporous activated carbonparticles and between about 2 and 30 percent mesoporous activated carbonparticles by weight. The active electrode material further includesbinder. The active electrode material may also include conductiveparticles, such as conductive carbon particles. In one implementation,the activated carbon may have between about 80 and 98 percentmicroporous activated carbon particles and between about 2 and 20percent mesoporous activated carbon particles by weight. In anotherimplementation, the activated carbon may have between about 85 and 95percent microporous activated carbon particles and between about 5 and15 percent mesoporous activated carbon particles by weight.

In one implementation, an electrochemical double layer capacitor mayinclude a first electrode comprising a first current collector and afirst film of active electrode material, the first film comprising afirst surface and a second surface, the first current collector beingattached to the first surface of the first film; a second electrodecomprising a second current collector and a second film of activeelectrode material, the second film comprising a third surface and afourth surface, the second current collector being attached to the thirdsurface of the second film; a porous separator disposed between thesecond surface of the first film and the fourth surface of the secondfilm; a container; an electrolyte; wherein: the first electrode, thesecond electrode, the porous separator, and the electrolyte are disposedin the container; the first film is at least partially immersed in theelectrolyte; the second film is at least partially immersed in theelectrolyte; the porous separator is at least partially immersed in theelectrolyte; each of the first and second films may include a mixturecomprising activated carbon, wherein the activated carbon has betweenabout 70 and 98 percent microporous activated carbon particles andbetween about 2 and 30 percent mesoporous activated carbon particles byweight. In one implementation, the electrode films further may includeconductive particles, such as conductive carbon. In one implementation,the electrode films further may include binder. In one implementation,the films are attached to respective collectors via a conductiveadhesive layer.

These and other features and aspects of the present invention will bebetter understood with reference to the following description, drawings,and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates selected operations of a process for making activeelectrode material in accordance with some aspects hereof, and

FIG. 2, which includes sub-part FIGS. 2A and 2B, illustrates across-section of respective electrode assemblies which may be used in anultracapacitor.

DETAILED DESCRIPTION

In this document, the words “implementation” and “variant” may be usedto refer to a particular apparatus, process, or article of manufacture,and not necessarily always to one and the same apparatus, process, orarticle of manufacture. Thus, “one implementation” (or a similarexpression) used in one place or context can refer to one particularapparatus, process, or article of manufacture; and, the same or asimilar expression in a different place can refer either to the same orto a different apparatus, process, or article of manufacture. Similarly,“some implementations,” “certain implementations,” or similarexpressions used in one place or context may refer to one or moreparticular apparatuses, processes, or articles of manufacture; the sameor similar expressions in a different place or context may refer to thesame or a different apparatus, process, or article of manufacture. Theexpression “alternative implementation” and similar phrases are used toindicate one of a number of different possible implementations. Thenumber of possible implementations is not necessarily limited to two orany other quantity. Characterization of an implementation as “anexemplar” or “exemplary” means that the implementation is used as anexample. Such characterization does not necessarily mean that theimplementation is a preferred implementation; the implementation may butneed not be a currently preferred implementation.

The expression “active electrode material” and similar phrases signifymaterial that provides or enhances the function of the electrode beyondsimply providing a contact or reactive area approximately the size ofthe visible external surface of the electrode. In a double layercapacitor electrode, for example, a film of active electrode materialincludes particles with high porosity, so that the surface area of theelectrode exposed to an electrolyte in which the electrode is immersedmay be increased well beyond the area of the visible external surface;in effect, the surface area exposed to the electrolyte becomes afunction of the volume of the film made from the active electrodematerial.

The meaning of the word “film” is similar to the meaning of the words“layer” and “sheet”; the word “film” does not necessarily imply aparticular thickness or thinness of the material. When used to describemaking of active electrode material film, the terms “powder,”“particles,” and the like refer to a plurality of small granules. As aperson skilled in the art would recognize, particulate material is oftenreferred to as a powder, grain, specks, dust, or by other appellations.References to carbon and binder powders throughout this document arethus not meant to limit the present implementations.

The references to “binder” within this document are intended to conveythe meaning of polymers, co-polymers, and similar ultra-high molecularweight substances capable of providing a binding for the carbon herein.Such substances are often employed as binder for promoting cohesion inloosely-assembled particulate materials, i.e., active filler materialsthat perform some useful function in a particular application.

The words “calender,” “nip,” “laminator,” and similar expressions mean adevice adapted for pressing and compressing. Pressing may be, but is notnecessarily, performed using rollers. When used as verbs, “calender” and“laminate” mean processing in a press, which may, but need not, includerollers. Mixing or blending as used herein may mean processing whichinvolves bringing together component elements into a mixture. High shearor high impact forces may be, but are not necessarily, used for suchmixing. Example equipment that can be used to prepare/mix the drypowder(s) hereof may include, in non-limiting fashion: a ball mill, anelectromagnetic ball mill, a disk mill, a pin mill, a high-energy impactmill, a fluid energy impact mill, an opposing nozzle jet mill, afluidized bed jet mill, a hammer mill, a fritz mill, a Warring blender,a roll mill, a mechanofusion processor (e.g., a Hosokawa AMS), or animpact mill.

Other and further definitions and clarifications of definitions may befound throughout this document. The definitions are intended to assistin understanding this disclosure and the appended claims, but the scopeand spirit of the invention should not be construed as strictly limitedto the definitions, or to the particular examples described in thisspecification.

Reference will now be made in detail to several implementations of theinvention that are illustrated in the accompanying drawings. The samereference numerals are used in the drawings and the description to referto the same or substantially the same parts or operations. The drawingsare in simplified form and not to precise scale. For purposes ofconvenience and clarity only, directional terms, such as top, bottom,left, right, up, down, over, above, below, beneath, rear, and front maybe used with respect to the accompanying drawings. These and similardirectional terms, should not be construed to limit the scope of theinvention.

Referring more particularly to the drawings, FIG. 1 illustrates selectedoperations of a dry process 100 for making active electrode material.Although the process operations are described substantially serially,certain operations may also be performed in alternative order, inconjunction or in parallel, in a pipelined manner, or otherwise. Thereis no particular requirement that the operations be performed in thesame order in which this description lists them, except where explicitlyso indicated, otherwise made clear from the context, or inherentlyrequired. Not all illustrated operations may be strictly necessary,while other optional operations may be added to the process 100. A highlevel overview of the process 100 is provided immediately below. A moredetailed description of the operations of the process 100 and variantsof the operations are provided following the overview.

In operation 105, activated carbon particles with different porositiesmay be provided. For the purposes of this application, micropores referto pores in activated carbon having a pore diameter of less than 2nanometers, mesopores refer to pores in activated carbon having a porediameter from 2 nanometers to 50 nanometers, and macropores refer topores in activated carbon having a pore diameter of greater than 50nanometers. A bulk activated carbon material may also be classified asmicroporous activated carbon material, mesoporous activated carbonmaterial, and macroporous activated carbon material. A microporousactivated carbon material refers to a bulk activated carbon materialhaving a majority of micropores (i.e., greater than 50 percent of itspores being micropores). A mesoporous activated carbon material refersto a bulk activated carbon material having a majority of mesopores. Amacroporous activated carbon material refers to a bulk activated carbonmaterial having a majority of macropores.

In operation 110, optional conductive particles, such as conductivecarbon particles with low contamination level and high conductivity orother conductive particles may be provided. In operation 115, binder maybe provided. In one or more implementations, and although one or more ofa variety of binders may be used as described elsewhere herein, thebinder may include polytetrafluoroethylene (also known as PTFE or by thetradename, “Teflon®”). In operation 120, one or more of the activatedcarbon, conductive carbon, and binder may be blended or mixed; typicallytwo or more may be mixed together. Alternatively, in certainimplementations one or more of these ingredients and/or operations maybe omitted.

More detailed descriptions of individual operations of the process 100in preferred and alternative forms are now set forth. As a firstexample, operation 105, in which activated carbon particles with betweenabout 70 and 98 percent microporous activated carbon particles andbetween about 2 and 30 percent mesoporous activated carbon particles byweight, is first described. Electrodes made from activated carbonparticles with between about 70 and 98 percent microporous activatedcarbon particles and between about 2 and 30 percent mesoporous activatedcarbon particles by weight tend to have better mobility of electrolytein which the electrodes are immersed and ions within the electrolyte toreduce or prevent local electrolyte starvation from occurring, than inthe case of activated carbon particles with a higher percentage ofmicroporous activated carbon. Accordingly, in some implementations theactivated carbon particles provided in operation 105 have between about70 and 98 percent microporous activated carbon particles and betweenabout 2 and 30 percent mesoporous activated carbon particles by weight.In some more specific implementations, activated carbon particlesprovided in the operation 105 have between about 80 and 98 percentmicroporous activated carbon particles and between about 2 and 20percent mesoporous activated carbon particles by weight of the activatedcarbon particles may. In another implementation, the activated carbonparticles provided in the operation 105 have between about 85 and 95percent microporous activated carbon particles and between about 5 and15 percent mesoporous activated carbon particles by weight

In operation 115, binders may be provided, for example: PTFE in granularpowder form, and/or various fluoropolymer particles, polypropylene,polyethylene, co-polymers, and/or other polymer blends. It has beenidentified, that the use of inert binders such as PTFE, tends toincrease the voltage at which an electrode including such an inertbinder may be operated. Such increase occurs in part due to reducedinteractions with electrolyte in which the electrode is subsequentlyimmersed. In one implementation, typical diameters of the PTFE particlesmay be in the five hundred micron range.

In the operation 120, activated carbon particles and binder particlesmay be blended or otherwise mixed together. In various implementations,proportions of activated carbon (comprising both microporous activatedcarbon and mesoporous activated carbon as described above) and bindermay be as follows: about 80 to about 97 percent by weight of activatedcarbon, about 3 to about 20 percent by weight of PTFE. Optionalconductive carbon could be added in a range of about 0 to about 15percent by weight. An implementation may contain about 89.5 percent ofactivated carbon, about 10 percent of PTFE, and about 0.5 percent ofconductive carbon. Other ranges are within the scope hereof as well.Note that all percentages are here presented by weight, though otherpercentages with other bases may be used. Conductive carbon may bepreferably held to a low percentage of the mixture because an increasedproportion of conductive carbon may tend to lower the breakdown voltageof electrolyte in which an electrode made from the conductive carbonparticles is subsequently immersed (alternative electrolyte examples areset forth below).

In an implementation of the process 100, the blending operation 120 maybe a “dry-blending” operation, i.e., blending of activated carbon,conductive carbon, and/or binder is performed without the addition ofany solvents, liquids, processing aids, or the like to the particlemixture. Dry-blending may be carried out, for example, for about 1 toabout 10 minutes in a mill, mixer or blender (such as a V-blenderequipped with a high intensity mixing bar, or other alternativeequipment as described further below), until a uniform dry mixture isformed. Those skilled in the art will identify, after perusal of thisdocument, that blending time can vary based on batch size, materials,particle size, densities, as well as other properties, and yet remainwithin the scope hereof.

In another implementation, the blending operation 120 may blendactivated carbon, conductive carbon, and/or binder together with theaddition of any solvents, liquids processing aids, or the like. Suchadditives, for example, may be helpful in forming an electrode filmdepending on the process used to ultimately form the film. Coating orextrusion film processes, for example, may require one or more additivesto be blended or otherwise mixed with the other materials.

As introduced above, the blended dry powder material or other blendedmaterials (e.g., including one or more dry or wet additive) may also oralternatively be formed/mixed/blended using other equipment. Suchequipment that can be used to prepare/mix the dry powder(s) or othermaterials hereof may include, for non-limiting examples: blenders ofmany sorts including rolling blenders and warring blenders, and mills ofmany sorts including ball mills, electromagnetic ball mills, disk mills,pin mills, high-energy impact mills, fluid energy impact mills, opposingnozzle jet mills, fluidized bed jet mills, hammer mills, fritz mills,roll mills, mechanofusion processing (e.g., a Hosokawa AMS), or impactmills. In an implementation, the dry powder material may be dry mixedusing non-lubricated high-shear or high impact force techniques. In animplementation, high-shear or high impact forces may be provided by amill such as one of those described above. The dry powder material orother blended material may be introduced into the mill, whereinhigh-velocities and/or high forces could then be directed at or imposedupon the dry powder material to effectuate application of high shear orhigh impact to the binder within the dry powder material or otherblended material. The shear or impact forces that arise during the drymixing process may physically affect the binder, causing the binder tobind the binder to and/or with other particles within the material.

Moreover, although additives, such as solvents, liquids, and the like,are not necessarily used in some implementations of the manufacture ofcertain electrode films disclosed herein, a certain amount of impurity,for example, moisture, may be absorbed by the active electrode materialfrom the surrounding environment. Those skilled in the art willunderstand, after perusal of this document, that the dry particles usedwith implementations and processes disclosed herein may also, prior tobeing provided by particle manufacturers as dry particles, havethemselves been pre-processed with additives and, thus, contain one ormore pre-process residues. For these reasons, one or more of theimplementations and processes disclosed herein may utilize a dryingoperation at some point before a final electrolyte impregnationoperation, so as to remove or reduce the aforementioned pre-processresidues and impurities. Even after one or more drying operations, traceamounts of moisture, residues and impurities may be present in theactive electrode material and an electrode film made therefrom.

It should also be noted that references to dry-blending, dry particles,and other dry materials and processes used in the manufacture of anactive electrode material and/or film do not exclude the use of otherthan dry processes, for example, this may be achieved after drying ofparticles and films that may have been prepared using a processing aid,liquid, solvent, or the like.

A product obtained through a process like process 100 may be used tomake an electrode film. The films may then be bonded to a currentcollector, such as a foil made from aluminum or another conductor. Thecurrent collector can be a continuous metal foil, metal mesh, ornonwoven metal fabric. The metal current collector provides a continuouselectrically conductive substrate for the electrode film. The currentcollector may be pretreated prior to bonding to enhance its adhesionproperties. Pretreatment of the current collector may include mechanicalroughing, chemical pitting, and/or use of a surface activationtreatment, such as corona discharge, active plasma, ultraviolet, laser,or high frequency treatment methods known to a person skilled in theart. In one implementation, the electrode films may be bonded to acurrent collector via an intermediate layer of conductive adhesive knownto those skilled in the art.

In one implementation, a product obtained from process 100 may be mixedwith a processing aid to obtain a slurry-like composition used by thoseskilled in the art to coat an electrode film onto a collector (i.e. acoating process). The slurry may be then deposited on one or both sidesof a current collector. After a drying operation, a film or films ofactive electrode material may be formed on the current collector. Thecurrent collector with the films may be calendered one or more times todensify the films and to improve adhesion of the films to the currentcollector.

In one implementation, a product obtained from process 100 may be mixedwith a processing aid to obtain a paste-like material. The paste-likematerial may be then be extruded, formed into a film, and deposited onone or both sides of a current collector. After a drying operation, afilm or films of active electrode material may be formed on the currentcollector. The current collector with the dried films may be calenderedone or more times to densify the films and to improve adhesion of thefilms to the current collector.

In yet another implementation, in a product obtained through the process100 the binder particles may include thermoplastic or thermosetparticles. A product obtained through the process 100 that includesthermoplastic or thermoset particles may be used to make an electrodefilm. Such a film may then be bonded to a current collector, such as afoil made from aluminum or another conductor. The films may be bonded toa current collector in a heated calendar apparatus. The currentcollector may be pretreated prior to bonding to enhance its adhesionproperties. Pretreatment of the current collector may include mechanicalroughing, chemical pitting, and/or use of a surface activationtreatment, such as corona discharge, active plasma, ultraviolet, laser,or high frequency treatment methods known to a person in the art.

Other methods of forming the active electrode material films with orwithout additives and attaching the films to the current collector mayalso be used.

FIG. 2, including sub-part FIGS. 2A and 2B, illustrates, in a high levelmanner, respective cross-sectional views of an electrode assembly 200which may be used in an ultracapacitor or a double layer capacitor. InFIG. 2A, the components of the assembly 200 are arranged in thefollowing order: a first current collector 205, a first active electrodefilm 210, a porous separator 220, a second active electrode film 230,and a second current collector 235. In some implementations, aconductive adhesive layer (not shown) may be disposed on currentcollector 205 prior to bonding of the electrode film 210 (or likewise oncollector 235 relative to film 230). In FIG. 2B, a double layer of films210 and 210A are shown relative to collector 205, and a double layer230, 230A relative to collector 235. In this way, a double-layercapacitor may be formed, i.e., with each current collector having acarbon film attached to both sides. A further porous separator 220A maythen also be included, particularly for a jellyroll application, theporous separator 220A either attached to or otherwise disposed adjacentthe top film 210A, as shown, or to or adjacent the bottom film 230A (notshown). The films 210 and 230 (and 210A and 230A, if used) may be madeusing particles of active electrode material obtained through theprocess 100 described in relation to FIG. 1. An exemplary double layercapacitor using the electrode assembly 200 may further include anelectrolyte and a container, for example, a sealed can, that holds theelectrolyte. The assembly 200 may be disposed within the container (can)and immersed in the electrolyte. In many implementations, the currentcollectors 205 and 235 may be made from aluminum foil, the porousseparator 220 may be made from one or more ceramics, paper, polymers,polymer fibers, glass fibers, and the electrolytic solution may includein some examples, 1.5 M tetramethylammonium tetrafluoroborate in organicsolutions, such as PC or Acetronitrile solvent. Alternative electrolyteexamples are set forth below.

Following are several non-limiting examples of aqueous electrolyteswhich may be used in double-layer capacitors or ultracapacitors hereof:1-molar Sodium sulphate, Na₂SO₄; 1-molar Sodium perchlorate, NaClO₄;1-molar Potassium hydroxide, KOH; 1-molar Potassium chloride, KCl;1-molar Perchloric acid, HClO₄; 1-molar Sulfuric acid, H₂SO₄; 1-molarMagnesium chloride, MgCl₂; and, Mixed aqueous 1-molar MgCl₂/H₂O/Ethanol.Some non-limitative nonaqueous aprotic electrolyte solvents which can beused in capacitors include: Acetonitrile; Gamma-butyrolactone;Dimethoxyethane; N,N,-Dimethylformamide; Hexamethyl-phosphorotriamide;Propylene carbonate; Dimethyl carbonate; Tetrahydrofuran;2-methyltetra-hydrofuran; Dimethyl sulfoxide; Dimethyl sulfite;Sulfolane (tetra-methylenesulfone); Nitromethane; and, Dioxolane.Further, some non-limiting examples of electrolyte salts which can beused in the aprotic solvents include: Tetraalkylammonium salts (such as:Tetraethylammonium tetrafluoroborate, (C₂H₅)₄NBF₄;Methyltriethylammonium tetrafluoroborate, (C₂H₅)₃CH₃NBF₄;Tetrabutylammonium tetrafluoroborate, (C₄H₉)₄NBF₄; and,Tetraethylammonium hexafluorophosphate (C₂H₅)NPF₆);Tetraalkylphosphonium salts (such as: Tetraethylphosphoniumtetrafluoroborate (C₂H₅)₄PBF₄; Tetrapropylphosphonium tetrafluoroborate(C₃H₇)₄PBF₄; Tetrabutylphosphonium tetrafluoroborate (C₄H₉)₄PBF₄;Tetrahexylphosphonium tetrafluoroborate (C₆H₁₃)₄PBF₄;Tetraethylphosphonium hexafluorophosphate (C₂H₅)₄PPF₆; and,Tetraethylphosphonium trifluoromethylsulfonate (C₂H₅)₄PCF₃SO₃; andLithium salts (such as: Lithium tetrafluoroborate LiBF₄; Lithiumhexafluorophosphate LiPF₆; Lithium trifluoromethylsulfonate LiCF₃SO₃).Additionally, some Solvent free ionic liquids which may be used include:1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl) imideEMIMBeTi; 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl imideEMIMIm; EMIIm; EMIBeti; EMIMethide; DMPIIm; DMPIBeti; DMPIMethide;BMIIm; BMIBeti; BMIMethide; PMPIm; and, BMPIm. Examples for use asAnions include: bis(trifluoromethylsulfonyl)imide (CF₃SO₂)₂N—;bis(perfluoroethylsulfonyl)imide (C₂F₅SO₂)₂N—; and,tris(trifluoromethylsulfonyl)methide (CF₃SO₂)₃C⁻. And, examples for useas Cations include: EMI: 1-ethyl-3-methylimidazolium; DMPI:1,2-dimethyl-3-propylimidazolium; BMI: 1-butyl-3-methylimidazolium; PMP:1-N-propyl-3-methylpyridinium; and, BMP: 1-N-butyl-3-methylpyridinium.

Electrode products that include an active electrode film attached to acurrent collector and/or a porous separator may be used in anultracapacitor or a double layer capacitor and/or other electricalenergy storage devices.

In some implementations using a process 100, wherein activated carbonwith between about 70 and 98 percent microporous activated carbonparticles and between about 2 and 30 percent mesoporous activated carbonparticles by weight or in some cases between about 80 and 98 percentmicroporous activated carbon particles and between about 2 and 20percent mesoporous activated carbon particles by weight or even betweenabout 85 and 95 percent microporous activated carbon particles andbetween about 5 and 15 percent mesoporous activated carbon particles byweight is used, a high performance ultracapacitor or double-layercapacitor product can be provided. Such a product further may includeabout 10 percent by weight binder, and about 0.5 percent by weightconductive particles, such as conductive carbon.

The inventive methods for making active electrode material, films ofthese materials, electrodes made with the films, and double layercapacitors employing the electrodes have been described above inconsiderable detail. This was done for illustrative purposes. Neitherthe specific implementations of the invention as a whole, nor those ofits features, limit the general principles underlying the invention. Inparticular, the invention is not necessarily limited to the specificconstituent materials and proportions of constituent materials used inmaking the electrodes. The invention is also not necessarily limited toelectrodes used in double layer capacitors, but extends to otherelectrode applications. The specific features described herein may beused in some implementations, but not in others, without departure fromthe spirit and scope of the invention as set forth. Many additionalmodifications are intended in the foregoing disclosure, and it will beappreciated by those of ordinary skill in the art that, in someinstances, some features of the invention will be employed in theabsence of other features. The illustrative examples therefore do notdefine the metes and bounds of the invention and the legal protectionafforded the invention, which function is served by the claims and theirequivalents.

1. A method of making an active electrode material, the methodcomprising: providing activated carbon having between about 70 and 98percent microporous activated carbon particles of a total amount ofactivated carbon by weight and between about 2 and 30 percent mesoporousactivated carbon particles of the total amount of activated carbon byweight; providing binder; and mixing the activated carbon and the binderto obtain a mixture.
 2. A method in accordance with claim 1, wherein theproviding activated carbon operation comprises providing activatedcarbon having between about 80 and 98 percent microporous activatedcarbon particles of the total amount of activated carbon by weight andbetween about 2 and 20 percent mesoporous activated carbon particles ofthe total amount of activated carbon by weight.
 3. A method inaccordance with claim 1, wherein the operation of providing theactivated carbon includes providing the total amount of activated carbonin amount of between about 80 and about 97 percent of the mixture byweight, and wherein the operation of providing the binder includesproviding binder in amount of between about 3 and about 20 percent ofthe mixture by weight.
 4. A method in accordance with claim 1, furthercomprising conductive particles.
 5. A method in accordance with claim 4,wherein the conductive particles comprise conductive carbon.
 6. A methodin accordance with claim 1, wherein the operation of mixing includes dryblending the activated carbon and the binder.
 7. A method in accordancewith claim 1, wherein the operation of mixing is performed withoutprocessing additives.
 8. A method in accordance with claim 1, whereinthe operation of mixing is performed with processing additives.
 9. Amethod in accordance with claim 1, further comprising forming anelectrode film from the mixture.
 10. An electrode comprising: a currentcollector; and a film of active electrode material attached to thecurrent collector, wherein the active electrode material comprises atotal amount of activated carbon having between about 70 and 98 percentmicroporous activated carbon particles of the total amount of activatedcarbon by weight and between about 2 and 30 percent mesoporous activatedcarbon particles of the total amount of activated carbon by weight. 11.The electrode of claim 10, wherein the total amount of activated carbonhas between about 70 and 98 percent microporous activated carbonparticles of the total amount of activated carbon by weight and betweenabout 2 and 30 percent mesoporous activated carbon particles of thetotal amount of activated carbon by weight.
 12. The electrode of claim10, wherein the active electrode material includes activated carbon anda binder, wherein the total amount of activated carbon is in an amountof between about 80 and about 97 percent of the film by weight, andwherein the binder is in an amount of between about 3 and about 20percent of the film by weight.
 13. The electrode of claim 10, whereinthe active electrode material is formed from a mixture of activatedcarbon and binder.
 14. An electrochemical double layer capacitorcomprising: a first electrode comprising a first current collector and afirst film of active electrode material, the first film comprising afirst surface and a second surface, the first current collector beingattached to the first surface of the first film, wherein the first filmcomprises a total amount of activated carbon having between about 70 and98 percent microporous activated carbon particles of the total amount ofactivated carbon by weight and between about 2 and 30 percent mesoporousactivated carbon particles of the total amount of activated carbon byweight; a second electrode comprising a second current collector and asecond film of active electrode material, the second film comprising athird surface and a fourth surface, the second current collector beingattached to the third surface of the second film; a porous separatordisposed between the second surface of the first film and the fourthsurface of the second film; a container; an electrolyte; wherein: thefirst electrode, the second electrode, the porous separator, and theelectrolyte are disposed in the container; the first film is at leastpartially immersed in the electrolyte; the second film is at leastpartially immersed in the electrolyte; the porous separator is at leastpartially immersed in the electrolyte; each of the first and secondfilms include a mixture of carbon and binder with a resulting ironcontent of about equal to or not exceeding about 20 parts per million.15. The capacitor of claim 14, wherein the films are attached torespective collectors via a conductive adhesive layer.
 16. The capacitorof claim 14, wherein the total amount of activated carbon has betweenabout 70 and 98 percent microporous activated carbon particles of thetotal amount of activated carbon by weight and between about 2 and 30percent mesoporous activated carbon particles of the total amount ofactivated carbon by weight.
 17. The electrode of claim 14, wherein theactive electrode material includes activated carbon and a binder,wherein the total amount of activated carbon is in an amount of betweenabout 80 and about 97 percent of the first film by weight, and whereinthe binder is in an amount of between about 3 and about 20 percent ofthe first film by weight.
 18. The capacitor of claim 14, wherein theactive electrode material is formed from a mixture of activated carbonand binder.